A hydrogen generating cathode is used for the electrolysis (electrolyzation) producing hydrogen, chlorine, caustic soda or the like by electrolyzing water or aqueous solutions of alkali metal compounds (typically, alkali metal chlorides). In electrolysis industry, the reduction of energy consumption, specifically, the reduction of the electrolysis voltage is a significant problem. Recently, as the method for electrolyzing aqueous alkali metal chloride solutions such as an aqueous sodium chloride solution, the ion-exchange membrane method predominates, and various investigations have hitherto been performed. When electrolysis is actually performed, in addition to the theoretically determined voltage required for the electrolysis of sodium chloride, the overvoltage of the anode reaction (generation of chlorine), the overvoltage of the cathode reaction (generation of hydrogen), the voltage due to the resistance of the ion-exchange membrane, and the voltage due to the inter-electrode distance between the anode and the cathode are required. When attention is paid to the overvoltage due to the electrode reaction, of these voltages, a noble metal-based electrode referred to as the so-called DSA (Dimensionally Stable Anode) has been developed as an anode for chlorine generation; in the electrode concerned, the chlorine overvoltage is reduced largely so as to be 50 mV or less.
On the other hand, also for a cathode involving hydrogen generation, recently from the viewpoint of energy saving, a cathode being low in hydrogen overvoltage and having durability has been demanded. As a hydrogen generating cathode, soft steel, stainless steel and nickel have been formerly used. In addition, the activation of the surface of these hydrogen generating cathodes to reduce the hydrogen overvoltage has been investigated, and for these techniques, many patent applications have been performed. Examples of the catalyst for the hydrogen generating cathode include nickel, nickel oxide, an alloy of nickel and tin, a combination of activated carbon and an oxide, ruthenium oxide and platinum. The catalyst layers including these catalysts are formed by alloy plating, dispersion composite plating, thermal decomposition, thermal spraying and combinations of these.
In Patent Literature 1 (Japanese Patent Laid-Open No. 2000-239882), a catalyst layer composed of a lanthanum metal-based compound and a platinum group compound is formed, as a catalyst composition, on a conductive substrate, and thus, a cathode having a low overvoltage is formed. In Patent Literature 2 (Japanese Patent Laid-Open No. 2008-133532), ruthenium nitrate and a carboxylic acid salt of lanthanum are applied onto a conductive substrate, and calcined in the atmosphere to form a catalyst layer, and thus, the catalyst layer is stabilized over a long term even in a high current density operation. In Patent Literature 3 (Japanese Patent Laid-Open No. 2008-240001), a hydrogen adsorption layer is formed on a catalyst layer, and thus, the hydrogen generation efficiency is improved.